The disclosure relates to a solenoid valve, particularly for an hydraulic braking system of a motor vehicle, having a valve sleeve, in which a pole core is fixed and an armature is arranged so that it is axially displaceable, wherein the armature comprises at least one longitudinal groove in the outer shell surface thereof, and wherein a disk spring is/can be braced between the armature and the pole core.
The disclosure further relates to a braking system, particularly for a motor vehicle, having at least one solenoid valve for controlling and/or regulating a pressure and/or a volumetric flow of a hydraulic medium of the braking system.
Solenoid valves and braking systems of the aforementioned type are known from the state of the art. Solenoid valves, which are designed as normally closed solenoid valves, are used, in particular, for safety-relevant brake applications, such as, for example, ABS or ESP systems (ABS=antilock braking system; ESP=electronic stability program). Such valves are capable of assuming at least two different hydraulic settings, for example open or closed, or they are also further adjustable through partial lifting between open and closed as so-called control valves. The closed position of the solenoid valve in the non-energized, i.e. unactuated state is usually ensured by way of a compression spring. A magnetic or electromagnetic actuator, which comprises an electromagnetic coil and magnetically active components in the solenoid valve, serves for switching or actuation of the solenoid valve. The components provided here in the valve are a pole core and an axially displaceable armature. On actuation, a pole core enclosed by the electromagnetic coil exerts a tensile force on the armature, in order to displace the latter axially, thereby exposing a valve opening. Such solenoid valves usually have a magnetic force characteristic such that the magnetic force increases very sharply (exponentially) as the working air gap diminishes, that is to say as the distance between the armature and the pole core diminishes. A known way of optimizing the magnetic force characteristic is to arrange a disk spring, which acts in parallel with the compression spring and which may be magnetizable, between the pole core and the armature. As the working air gap diminishes here, a radially running secondary flow occurs, the radial component of which no longer contributes to the axial force and allows only a shallow rise in the latter—despite the diminishing working air gap. It is thereby possible to exert a beneficial influence on the magnetic force, so that it approximates to the ideal state.
Providing the armature with at least one longitudinal groove, which serves to equalize the hydraulic pressure between the working air gap and the pressure chamber at the valve tip assigned to the armature, is also known. In hitherto known solenoid valves, however, the longitudinal groove means that at its outer circumference the spring disk does not bear fully on the end face of the armature facing the pole core. Particularly in the case of a disk spring having one or more radial recesses, the spring characteristic would depend overall on the rotational position of the disk spring relative to the armature. Furthermore, the longitudinal groove reduces the fatigue strength of the disk spring, since the material stress increases significantly due to the deformation introduced via the longitudinal groove.